This is an incredible cheap solution for using the old M42 glass. I found myself using it more than any of my newer glass just for the Bokeh and warmth. For the price and quality, I'd highly recommend it!
This adaptor is a great fit on my GH5 for my Helios 44-M. No light leaks, easy to fit, doesn’t come loose when changing the lens. You do have to adjust the ibis (double the focal length, I use 116, so it’s a definite portrait lens) but it gives a new lease of life to a lovely lens. Everything works fine. Well worth it and gives you a great vintage lens in your kit.